1. Field of the Invention
This invention relates to a method of forming two or more coating layers on a fiber.
2. Description of the Prior Art
Dual coated optical fibers are becoming increasingly used to obtain design flexibility and improved performance. Typically, a first or primary coating layer is applied that comprises a low-modulus material. Such a material reduces microbending losses associated with the cabling, installation, or environmental changes during the service life of the optical fiber. An outer or secondary coating layer is applied onto the primary layer. The outer coating layer is usually of a higher modulus material to provide for abrasion resistance for the fiber and primary coating layer. The first coating layer can be applied in an open cup applicator which may have a rigid or flexible tip. It is also known to use pressurized applicators for increasing the coating speed and to reduce the entrapment of bubbles, etc.; see, for example, U.S. patent application Ser. No. 257,354, filed Apr. 24, 1981, now U.S. Pat. No. 4,374,161, coassigned with the present invention. In the prior art, the secondary coating layer has typically been applied by techniques that substantially duplicate the application of the first coating layer; that is, upon the exit of the fiber from a first coating reservoir, the fiber enters a second coating reservoir containing the secondary coating material; see, for example, "Double Layer Silicone Coating With Double Cone Nozzle In-Line With Optical Fiber Drawing," by M. Sato et al, in the Proceedings Of The Fifth European Conference On Optical Communication, page 5.6-1 (Amsterdam, 1979).
It is desirable to have improved methods of forming multiple coatings on a fiber.